Hypokalemia in Athletes: Causes and the Link to Drugs and Supplements
Potassium keeps nerves firing and the heart beating in rhythm. Healthy athletes rarely become seriously deficient from training alone, but low potassium, or hypokalemia, appears surprisingly often in sports where people manipulate weight and water, or use drugs that move potassium around the body. This article explains the causes, why some substances are particularly dangerous and what warning signs should not be ignored.
Potassium basics
About 98 percent of the body's potassium is inside cells, mostly in muscle. Only a small fraction circulates in the blood, where the normal range is about 3.5 to 5.0 mmol/L (equivalent to mEq/L). Hypokalemia is usually defined as a level below 3.5 mmol/L; values below 2.5 mmol/L are considered severe and can be life-threatening.
The steep difference between potassium inside and outside cells sets the electrical charge across cell membranes. The sodium–potassium pump maintains that gradient, a process Clausen reviewed in detail in the context of skeletal muscle contractility. When blood potassium falls, nerves and muscles become less excitable, while heart cells become electrically unstable.
Because the blood holds so little potassium, small shifts between cells and blood can cause large changes in the measured level. Some causes of hypokalemia therefore reflect potassium moving into cells rather than being lost from the body.
The US National Academies set Adequate Intakes of 3,400 mg per day for adult men and 2,600 mg for adult women. Many Americans eat less than this, but diet alone seldom produces clinical hypokalemia in people with healthy kidneys.
Causes related to training and diet
Sweat contains potassium, though much less than sodium. Very long sessions in the heat can cause measurable losses, but true hypokalemia from sweating alone is uncommon in well-nourished athletes. It is more likely when heavy sweating combines with very low food intake.
Prolonged vomiting or diarrhea, including from gastroenteritis while traveling, can rapidly deplete potassium. So can very low-carbohydrate or fasting regimens during the early phase, when the kidneys excrete more electrolytes.
Eating disorders, which are more prevalent in weight-sensitive and aesthetic sports, are a major cause of hypokalemia. Self-induced vomiting and laxative misuse cause large potassium losses and are associated with dangerous heart rhythm disturbances.
Excessive black licorice consumption, which contains glycyrrhizin, can mimic a hormone excess that drives potassium loss through the kidneys. It is an underappreciated cause, especially in people who consume licorice-flavored products daily.
Drugs and substances that lower potassium
The most important causes in sport are pharmacological. Cadwallader and colleagues reviewed diuretic misuse in sport, noting that athletes use them to lose weight quickly before weigh-ins or competitions and to dilute urine to mask other drugs. Loop and thiazide diuretics increase potassium loss through the kidneys, and hypokalemia is one of their best-known adverse effects. Diuretics are prohibited at all times under the WADA Code.
Beta-2 agonists, including asthma inhalers at high doses and clenbuterol, push potassium into cells. A classic study by Brown and colleagues showed that even circulating epinephrine at stress levels lowered blood potassium via beta-2 receptors. Clenbuterol, misused for fat loss and not approved for human use in the US, has been linked to hypokalemia, tachycardia and cardiac injury in case reports.
Insulin moves potassium into cells along with glucose. Insulin misuse in bodybuilding can cause sudden hypokalemia as well as severe hypoglycemia. Both effects can be fatal; deaths from insulin misuse among non-diabetic users have been reported, and there is no "safe" way to use it outside medical care.
| Substance | Mechanism | Main dangers |
|---|---|---|
| Loop and thiazide diuretics | Increased kidney potassium loss | Arrhythmia, dehydration, kidney injury |
| Beta-2 agonists (clenbuterol, high-dose inhalers) | Shift into cells | Tachycardia, cardiac damage |
| Insulin (non-medical use) | Shift into cells | Hypoglycemia, arrhythmia, death |
| Laxatives | Gut losses | Arrhythmia, chronic bowel damage |
| High-dose caffeine and stimulants | Shift into cells | Arrhythmia, especially combined with other drugs |
| Thyroid hormone misuse | Shift into cells, increased metabolism | Periodic paralysis, atrial fibrillation |
Several of these are often combined before physique competitions, multiplying the risk. Deaths of bodybuilders around competition time have been associated with diuretic use and electrolyte disturbances.
Symptoms and heart risk
Mild hypokalemia may cause no symptoms. As levels fall, people may notice:
- muscle weakness, fatigue and heaviness in the legs;
- muscle cramps or twitching;
- constipation and bloating;
- palpitations or an irregular heartbeat;
- in severe cases, paralysis, breathing difficulty and muscle breakdown (rhabdomyolysis).
The heart is the most serious concern. Low potassium causes characteristic ECG changes and raises the risk of ventricular arrhythmias, which can lead to sudden cardiac arrest. Risk is higher in people with heart disease, those taking digoxin and anyone combining multiple potassium-lowering substances.
Diagnosis, treatment and prevention
Hypokalemia is diagnosed with a blood test, often as part of a basic metabolic panel. Physicians also check magnesium, since low magnesium makes potassium hard to correct, and may order an ECG and urine potassium to determine whether losses are from the kidneys or gut. Reviews by Gennari and by Kardalas and colleagues outline this diagnostic approach.
Treatment depends on severity. Mild cases are often managed with oral potassium and treating the cause. Severe hypokalemia or ECG changes require urgent hospital care with monitored intravenous replacement, since giving potassium too quickly is itself dangerous.
Over-the-counter potassium supplements in the US are limited to small amounts per serving, largely because concentrated potassium can irritate the gut and, in people with kidney problems or on certain blood pressure drugs, cause dangerously high levels. Self-treating with large doses is not advisable.
For most athletes, prevention means eating potassium-rich foods such as potatoes, beans, bananas, leafy greens, yogurt and fruit, staying adequately fueled and avoiding diuretics, laxatives and other substances used to manipulate weight or appearance.
Conclusions of the Editorial Team
Training and sweating rarely cause significant hypokalemia in well-fed athletes. The most serious cases arise from substances: diuretics, beta-2 agonists such as clenbuterol, insulin, laxatives and thyroid hormone, often combined during weight cuts or competition preparation.
Because low potassium can trigger fatal arrhythmias, symptoms such as palpitations or unusual weakness should prompt immediate medical evaluation, not self-treatment with supplements.
Consider also reading our articles on muscle cramps in athletes, the risks of making weight with diuretics and how to interpret a basic metabolic panel.
References
- Gennari FJ. Hypokalemia. N Engl J Med. 1998;339(7):451–458.
- Kardalas E, Paschou SA, Anagnostis P, et al. Hypokalemia: a clinical update. Endocr Connect. 2018;7(4):R135–R146.
- Cadwallader AB, de la Torre X, Tieri A, Botrè F. The abuse of diuretics as performance-enhancing drugs and masking agents in sport doping: pharmacology, toxicology and analysis. Br J Pharmacol. 2010;161(1):1–16.
- Brown MJ, Brown DC, Murphy MB. Hypokalemia from beta2-receptor stimulation by circulating epinephrine. N Engl J Med. 1983;309(23):1414–1419.
- Clausen T. Na+-K+ pump regulation and skeletal muscle contractility. Physiol Rev. 2003;83(4):1269–1324.
- National Academies of Sciences, Engineering, and Medicine. Dietary Reference Intakes for Sodium and Potassium. Washington, DC: National Academies Press; 2019.
